scholarly journals Spin-resolved Alignment and Orientation Effects in Atomic Collisions

1996 ◽  
Vol 49 (2) ◽  
pp. 301 ◽  
Author(s):  
Klaus Bartschat ◽  
Nils Andersen
Keyword(s):  
Density Matrix ◽  
Stokes Parameters ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Matrix Elements ◽  
Atomic Ensembles ◽  
Atomic Collisions ◽  
Orientation Effects ◽  
Scattering Experiment ◽  
Orientation Parameters

The density matrix parametrisation of collisionally excited atomic ensembles is generalised to account for projectile and target spin polarisations. The density matrix elements, containing spin-resolved alignment and orientation parameters, can be determined by measurements of the 'generalised Stokes parameters' introduced by Andersen and Bartschat (1994) to describe scattered-projectile-polarised-photon coincidence experiments. Focusing on electron impact excitation of light alkali-type targets and mercury, the present experimental status of such experiments is reviewed, in particular with regard to the 'perfect scattering experiment' whereby all independent scattering amplitudes are determined.

Complete experiments in electron–atom impact excitation: present status and future prospects

1996 ◽  
Vol 74 (11-12) ◽  
pp. 929-943
Author(s):  
Nils Andersen ◽  
Klaus Bartschat
Keyword(s):  
Review Paper ◽  
Stokes Parameters ◽  
Impact Excitation ◽  
Future Prospects ◽  
Electron Atom ◽  
Scattering Experiment ◽  
Spin Polarized ◽  
Common Framework ◽  
Theoretical Results ◽  
Present Understanding

An overview is given of the present understanding of excitation in electron–atom collisions, with particular emphasis on the extent to which a "perfect scattering experiment" in the Bederson sense has been achieved. Recent experimental and theoretical results are put into a common framework, generalizing the ideas and systematics, presented in a review paper, of the case of excitation by spin-polarized electron beams. For various levels of complexity, complete sets of coherence parameters are suggested, and their relationships to generalized Stokes parameters and generalized STU parameters are pointed out.

Excitation from metastable 23S states of helium by electrons and positrons

1996 ◽  
Vol 74 (7-8) ◽  
pp. 521-526 ◽  
Author(s):  
Surbhi Verma ◽  
Rajesh Srivastava
Keyword(s):  
Electron Impact ◽  
Cross Sections ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Many Body ◽  
Many Body Theory ◽  
Electrons And Positrons ◽  
Body Theory ◽  
Orientation Parameters ◽  
Approximation Calculation

Our recent distorted-wave approximation calculation for the electron-impact excitation cross sections of the helium atom from its 23S state to upper states was extended to obtain alignment and orientation parameters for n3P (n = 2, 3, 4) excitations. Further, similar results are obtained by considering the excitation by impact of positrons. The calculated alignment and orientation results are compared with the only available theoretical electron-impact results obtained using first-order many-body theory.

Review of advances in describing the 31D-state excitation of helium

1996 ◽  
Vol 74 (11-12) ◽  
pp. 906-913
Author(s):  
J. F. Williams ◽  
A. G. Mikosza ◽  
J. B. Wang
Keyword(s):  
Scattering Amplitudes ◽  
Partial Cross Section ◽  
Stokes Parameters ◽  
Impact Excitation ◽  
Electron Impact Excitation ◽  
Scattered Electron ◽  
Close Coupling ◽  
Natural Frame ◽  
Electron Photon

Recent advances in describing the electron impact excitation of the 31D state of helium are reported for an incident energy of 40 eV and scattering angles from 10° to 40°. Measurements of the Stokes parameters have been made using the polarized photon–photon and electron–photon coincidence techniques. The partial cross section σm for the magnetic sublevels in the collision frame indicate that the m = 0 excitation is favoured. For the above scattering kinematics the data are in agreement with convergent close coupling calculations. The deduced scattering amplitudes, in the natural frame, show that the m = 2 excitation becomes dominant at the larger angles. Progress is reported on the complete determination of the scattering amplitudes and their relative phases using the triple-coincident detection of the scattered electron with the two sequential cascading photons.

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